Specific Modeling Issues on an Adaptive Winglet Skeleton

Abstract

Morphing aeronautical systems may be used for a number of aims, ranging from improving performance in specific flight conditions, to keeping the optimal efficiency over a certain parameters domain instead of confining it to a single point, extending the flight envelope, and so on. An almost trivial statement is that traditional skeleton architectures cannot be held as a structure modified from being rigid to deformable. That passage is not simple, as a structure that is able to be modified shall be designed and constructed to face those new requirements. What is not marginal, is that the new configurations can lead to some peculiar problems for both the morphing and the standard, supporting, elements. In their own nature, in fact, adaptive systems are designed to contain all the parts within the original geometry, without any “external adjoint”, such as nacelles or others. Stress and strain distribution may vary a lot with respect to usual structures and some particular modifications are required. Sometimes, it happens that the structural behavior does not match with the common experience and some specific adjustment shall be done to overcome the problem. What is reported in this paper is a study concerning the adaptation of the structural architecture, used to host a winglet morphing system, to make it accomplish the original requirements, i.e., allow the deformation values to be under the safety threshold. When facing that problem, an uncommon behavior of the finite element (FE) solver has been met: the safety factors appear to be tremendously dependent on the mesh size, so as to raise serious questions about the actual expected value, relevant for the most severe load conditions. On the other side, such singularities are more and more confined into single points (or single lines), as the mesh refines, so to evidence somehow the numerical effect behind those results. On the other side, standard engineering local methods to reduce the abovementioned strain peaks seem to work very well in re-distributing the stress and strain excesses to the whole system domain. The work does not intend to give an answer to the presented problem, being instead focused on describing its possible causes and its evident effects. Further work is necessary to detect the original source of such inconsistencies, and propose and test operative solutions. That will be the subject of the next steps of the ongoing research.

A Preliminary Technology Readiness Assessment of Morphing Technology Applied to Case Studies

“…Within the framework of the Clean Sky 2 REG IADP, the design of a fault-tolerant adaptive winglet concept was addressed to enhance the wing’s aerodynamic performance in off-design conditions and reduce maneuver loads of a turboprop regional aircraft. The integrated design of the adaptive winglet is detailed in [ 32 , 33 , 34 ]. The adaptive winglet incorporates two “finger-like” mechanisms, shown in Figure 5 , allowing shape adaptation of two movable surfaces (upper and lower tabs), each controlled by an independent electromechanical chain, and embedded into its main body [ 27 , 35 , 36 ].…”

“…As the former, it has been developed within the Airgreen 2 project. The technological capability has been widely addressed and extensively documented, [ 27 , 32 , 33 , 34 , 35 , 36 ]. A full-scale prototype of the functional winglet was tested in a relevant lab environment, under the design limit loads.…”

Editorial for the Special Issue “Aircraft Modeling and Simulation”

“…In the second group, focused on structural dynamics modeling area, two articles were published on an adaptive winglet finite element model (FEM) issue [3] and on the modeling of an oleo-pneumatic landing gear using MATLAB instead of FEM, which was considered as one of the originalities of this paper [4].…”

“…Among green aircraft technologies, one might include morphing aircraft systems development. Morphing or adaptive wing and winglets are able to change their structural shapes using actuators, sensors, and controls technologies in order to obtain better aerodynamic performances for the aircraft, as shown in the aerodynamics studies for morphing wings [1] and in the structural studies of an adaptive winglet [3].…”

“…The finite element modeling (FEM) issues for an adaptive winglet skeleton design at CIRA are discussed by [3]. For example, in this paper, a study was presented on the structural architecture adaptation for a winglet morphing system in order to allow its deformations within the safety margins.…”